Multiple stage, hydraulic jet propulsion apparatus for water craft



y 4, 1967 G. R. ASCHAUER 3,328,961

MULTIPLE STAGE, HYDRAULIC JET PROPULSION INVENTOK: 6-. R l scmqusa Filed Oct. 13, 1965 APPARATUS FOR WATER CRAFT United States Patent 3,328,961 MULTIPLE STAGE, HYDRAULIC JET PROPULSION APPARATUS FOR WATER CRAFT George R. Aschauer, Racine, Wis., assignor to Twin Disc Clutch Company, Racine Wis., a corporation of Wisconsln Filed Oct. 13, 1965, Ser. No. 495,640 Claims. (Cl. 60222) .which the second stage impeller is driven faster than the first stage impeller and the housing which surrounds the impellers converges toward the discharge end thereof. Theresult is a particularly efricient propulsion unit.

These and other objects and advantages of the present invention will appear as this disclosure progresses, reference being had to the accompanying drawings in which:

The figure is a longitudinal cross sectional view through a jet propulsion unit embodying the present invention.

In the design of marine jets of the type to which the present invention relates, the maximum propulsive efficiency depends among "other things, on the unit size and weight, g.p.m. of water flow, boat stall thrust and accelerating capability and allowable specific speed. High efi'iciency requires large flow of water and low jet velocity, consequently low jet pressure. Specific speed is represented by the known formula r.p.rn. vg.pm. where r.p.m. is the speed of the impeller, g.p.m. is the water flowing through and H is pressure head in feet of water generated by the pump.

It is desirable to have the highest practical water mass flow, and in order to have a specific speed (Ns) which is of a reasonably low value, the present invention utilizes a large diameter, low speed impeller. As the atmospheric pressure is the only thing that pushes the water into the intake opening when the craft is stationary, the large impeller design provides a large intake area and consequently good initial force due to atmospheric pressure to thereby push water into the intake. This permits use of a lower specific speed (Ns) value, which is desirable, because the rpm. can be less.

The quantity of water (mass) flowing through the unit should be as great as possible but is limited due to the physical strength and size of the water-borne craft.

Furthermore, in order to have adequate pressure rise through the propulsion unit, more than one stage is required, that is, the velocity of the water mass flow through the unit must be raised in stages.

Prior art propulsion units have of course used multiplestages but these stages have been of the same size and speed as one another. As only a low pressure rise can be obtained across the first stage due to the previously mentioned limitation of atmospheric push at the intake, the subsequent stages are also only low pressure rise stages because they all have the same flow (g.p.m.) and speed (r.p.m.). In order to keep the specific speed (Ns) value down to a low, practical value, it is necessary to keep the ratio of the net inlet head (Hsv) to pump generated head (H) near unity. In other words, it is desirable to balance out the total pressure rise through the unit in accordance with the inlet head (Hsv) for one reason, to prevent cavitation.

Patented July 4, 1967 In accordance with the present invention, the rpm. speed of the second stage impeller is greater than the first stage and furthermore the cross sectional area of the impeller housing decreases in a direction approaching the discharge end. This results in a high speed pumping unit with a corresponding high pressure-rise through the unit.

Referring now to the drawings, the propulsion unit U with a housing H is mounted with its intake 1 flush with the bottom 2 of the water craft C, and the discharge end 3 of the housing extends through the stem 4 of the craft in accordance with conventional practice. A nozzle N extends rearwardly beyond the stern for receiving the stream of water from the housing in the boat and discharging it to propel, steer or reverse the boat in the known manner. The nozzle may be of the type shown in my co-pending US. application Ser. No. 207,642, filed July 5, 1962 and entitled Jet Propelled Water Craft, which issued May 17, 1966 as Patent No. 3,251,185.

A power plant 5 drives the drive shaft 6 and a gear reduction means 7 is also driven from the shaft 6 and it in turn drives the drive leeve 8 within the housing H.

A first stage impeller 10 is fixed to the sleeve 8 and driven thereby to form a low speed pump or impeller.

A second stage impeller 12 is fixed to and driven by the shaft 6 to form the high speed pump or impeller.

The outer ends of the impellers are free or unsupported by a surrounding ring, and these ends are tapered rearwardly to define an impeller periphery which complements and is located closely adjacent to the internal shape of the housing in which they are mounted, as will appear.

Fixed stator blades 14 aresecured within the housing and are located behind the first stage impeller 10, and the hub 14a of these blades forms a support for the sleeve bearing 14b in which the rear end of the drive sleeve 8 is rotatably mounted.

Fixed stator blades 15 are fixed within the housing and directly behind the second stage impeller and the central hub 15a of these blades has a sleeve bearing 15b therein which rotatably supports the rear end of the drive shaft 6.

These stators act to straighten out the flow of water after it leaves the impellers, that is, they reduce the circular movement or spin of the water and direct it rearwardly.

The second impeller 12 may be of smaller diameter than the first stage impeller 10 and as previously menportion 18 may be of generally constant cross sectional area in a rearward direction. It will be noted, however, that subsequent portions of the housing as it extends rearwardly from the intake side 19 of the first stage impeller may converge or decrease in cross sectional area until it is rearward of the last impeller. The housing then converges up to the discharge end 3 of the unit.

The housing closely surrounds and complements the peripheral shape of the impellers.

The eye of the pump or unit U is the shaft 6, and when the craft is at the dock the net inlet head Ilsv at pump inlet is less than atmospheric because this pump eye is above the water level and also because of inlet friction flow losses due to bends, intake grill and other obstructions and disturbances.

With the present invention, a multiple-stage hydraulic jet propulsion unit is provided which is particularly efficient at operating speed. In addition, when the craft is at dock, the unit will operate with only minor cavitation.

Various modes of carrying out the invention are contemplated as being Within the scope of the "following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A multi-stage, hydraulic jet propulsion unit for waterborne craft comprising, a housing having a forward intake portion for receiving water and a rearward discharge portion for discharging water rearwardly of the stern of the craft, and said housing having a rearwardly converging portion, a first stage impeller mounted within said converging portion for being rotationally driven, a second stage impeller mounted within said converging portion and located rearwardly of and of smaller diameter than said first stage impeller and in co-axial alignment therewith, said housing closely surrounding said impellers in complementary converging relationship therewith, the flow rate of the water through the first stage impeller being the same as that through said second stage impeller and means for rotationally driving said second stage impeller faster than said first stage impeller.

2. A unit as defined in claim 1 including stator blades fixed within said converging portion of said housing and located between said impellers and also rearwardly of said second stage impeller for straightening out the flow of water.

3. A multi-stage, hydraulic jet propulsion unit for water-borne craft comprising, a housing having an inlet flush with the bottom of said craft for receiving water and a rearwardly and also an upwardly inclined forward portion extending from said inlet, said housing having an intermediate portion which converges rearwardly, and a rear discharge portion for discharging water rearwardly of the stern of the craft, a first stage impeller and a second stage impeller both mounted within said converging portion for being rotationally driven, said second stage impeller located rearwardly of and of smaller diameter than said first stage impeller and in co-aXial alignment therewith, said housing closely surrounding said impellers in complementary converging relationship therewith, the flow rate of the water through the first stage impeller being the same as that through said second stage impeller and means for rotationally driving said second stage impeller faster than said first stage impeller.

4. A unit as defined in claim 3 including stator blades fixed within said converging housing portion and located rearwardly of each of said impellers.

5. A multi-stage, hydraulic jet propulsion unit for water-borne craft comprising, a housing having an inlet flush with the bottom of said craft for receiving water and a forward portion extending rearwardly and upwardly from said inlet, said housing also having a rearwardly converging portion, and a rear discharge portion, a nozzle connected to said discharge portion whereby said housing discharges water into said nozzle, a first stage impeller and a second stage impeller both mounted within said converging portion for being rotationally driven, said second stage impeller located rearwardly of and of smaller diameter than said first stage impeller and in co-axial alignment therewith, stator blades fixed within said converging housing portion and located rearwardly of each of said impellers, said housing closely surrounding said impellers in complementary converging relationship therewith, the flow rate of the water through the first stage impeller being the same as that through said second stage impeller and means including an engine and gear reduction unit for rotationally driving said second stage impeller faster than said first stage impeller.

6. A multi-stage, hydraulic jet propulsion unit for water-borne craft comprising, a housing having a forward intake portion for receiving water and a rearward discharge portion for discharging water rearwardly of the stern of the craft, a first stage impeller mounted within said housing for being rotationally driven, a second stage impeller mounted within said housing and located rearwardly of said first stage impeller and in co-axial therewith, said housing closely surrounding said impellers in complementary relationship therewith, the flow rate of the water through the first stage impeller being the same as that through said second stage impeller and means for rotationally driving said second stage impeller faster than said first stage impeller.

7. A unit as defined in claim 6 .including stator blades fixed within said housing and located between said impellers and other stator blades located rearwardly of said second stage impeller for straightening out the flow of water.

8. A unit as defined in claim 6 further characterized in that said housing has an inlet in the bottom of said craft and also a rearwardly and upwardly inclined forward portion extending from said inlet.

9. A unit as defined in claim 8 including stator blades fixed within said housing and located rearwardly of each of said impellers.

10. The propulsion unit as defined in claim 9 including a nozzle connected to said discharge portion whereby said housing discharges water into said nozzle, and said means for driving said impellers includes an engine and gear reduction unit.

References Cited UNITED STATES PATENTS 1,316,139 9/1919 Cake 230l23 X 2,981,464 4/1961 Om'ohundro 230-123 X 3,083,529 4/1963 Hamilton -221 3,143,857 8/1964 Eaton 60-221 OTHER REFERENCES Yachting Magazine, November 1959, volume 106, N0. 5 (pages and 71 relied on).

CARLTON R. CROYLE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 328, 961 Dated July 4, 1967 Invencor(s) George R. Aschauer- It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 4., at the end of line 18, add the word --a1ignment--- Signed and sealed this 29th day of February 1972.

(SEAL) Attest;

EDWARD M. FLETCHER, JR. Q ERT GOTTSCHALK Attesting Officer- Commissioner of Patent 3 

1. A MULTI-STAGE, HYDRAULIC JET PROPULSION UNIT FOR WATERBORNE CRAFT COMPRISING, A HOUSING HAVING A FORWARD INTAKE PORTION FOR RECEIVING WATER AND A REARWARD DISCHARGE PORTION FOR DISCHARGING WATER REARWARDLY OF THE STERN OF THE CRAFT, AND SAID HOUSING HAVING A REARWARDLY CONVERGING PORTION, A FIRST STAGE IMPELLER MOUNTED WITHIN SAID CONVERGING PORTION FOR BEING ROTATIONALLY DRIVEN, A SECOND STAGE IMPELLER MOUNTED WITHIN SAID CONVERGING PORTION AND LOCATED REARWARDLY OF AND OF SMALLER DIAMETER THAN SAID FIRST STAGE IMPELLER AND IN CO-AXIAL ALIGNMENT THEREWITH, SAID HOUSING CLOSELY SURROUNDING SAID IMPELLERS IN COMPLEMENTARY CONVERGING RELATIONSHIP THEREWITH, THE FLOW 